This will happen if you are already logged in as a constituent. To log in as an admin, you can either do it from another browser, or you can log out of the constituent first and then browse to the admin login page. If you don't see a logout button, then you can perform the following URL hack:
  1. Delete everything after the /site/ parameter
  2. Add UserLogin?logout=true
  3. The completed URL might look something like this:
This URL logs you out of Luminate and will redirect you to your homepage at which point you should now be able to log in as an administrator.